The present invention relates to a parallel power supply system for providing a stable output voltage, and especially to a parallel power supply system with an over-voltage protection circuit for providing a stable output voltage.
FIG. 1 shows a parallel power supply system according to the prior art. Please refer to FIG. 1. A typical parallel power supply system for providing a stable DC output voltage includes a first power supply 11, a second power supply 12, a first isolated diode 21, a second isolated diode 22, a first low pass filter 31, a second low pass filter 32, a first voltage feedback controller 41, and a second voltage feedback controller 42. The first power supply 11 has a first output terminal for providing a first DC output voltage and a first ground terminal electrically connected to ground. The second power supply 12 has a second output terminal for providing a second DC output voltage and a second ground terminal electrically connected to ground. The first isolated diode 21 has an anode end electrically connected to the first output terminal of the first power supply 11. The second isolated diode 22 has an anode end electrically connected to the second output terminal of the second power supply 12, and a cathode end electrically connected to a cathode end of the first diode 21 for forming a node 5 which is an output Vo of the parallel power supply system. The first voltage feedback controller 41 is electrically connected to the output Vo for providing a first control signal to control the first DC output voltage of the first power supply 11 at a predetermined value. The second voltage feedback controller 42 is electrically connected to the output Vo for providing a second control signal to control the second DC output voltage of the second power supply 12 at the predetermined value. During the period that the first power supply 11 is under an abnormal operation, the first power supply 11 keeps the first DC output voltage greater than the predetermined value. Owing to the negative feedback control, the second voltage feedback controller 42 will provide the second control signal to decrease the second DC output voltage in order to maintain the DC output voltage at the predetermined value. Thereby, the second power supply 12 will be shutdown. In the same reason, during the period that the second power supply 12 is under an abnormal operation, and the second power supply 12 keeps the second DC output voltage greater than the predetermined value, the first power supply 11 will be shutdown owing to the negative feedback control.
It is therefore attempted by the applicant to deal with the above situation encountered with the prior art.
It is therefore an object of the present invention to propose a parallel power supply system with an over-voltage protection circuit that has two bypass diodes used for forming a bypass connection which operates during the over-voltage outputting period.
According to an aspect of the present invention, the parallel power supply system with an over-voltage protection circuit for providing a stable DC output voltage includes a first power supply having a first output terminal for providing a first DC output voltage and a first ground terminal electrically connected to ground, a second power supply having a second output terminal for providing a second DC output voltage and a second ground terminal electrically connected to ground, a first diode having an anode end electrically connected to the first output terminal of the first power supply, a second diode having an anode end electrically connected to the second output terminal of the second power supply, and a cathode end electrically connected to a cathode end of the first diode for forming a node which is an output of the parallel power supply system, a first voltage feedback controller electrically connected to the first DC output voltage for providing a first control signal to control the first DC output voltage of the first power supply at a predetermined value, a second voltage feedback controller electrically connected to the second DC output voltage for providing a second control signal to control the second DC output voltage of the second power supply at the predetermined value, a first resistor having one end electrically connected to the node and the other end electrically connected to an input terminal of the first voltage feedback controller, a second resistor having one end electrically connected to the node and the other end electrically connected to an input terminal of the second voltage feedback controller, a third diode having an anode end electrically connected to the input terminal of the first voltage feedback controller and a cathode end electrically connected to the first output terminal of the first power supply, and a fourth diode having an anode end electrically connected to the input terminal of the second voltage feedback controller and a cathode end electrically connected to the second output terminal of the first power supply, wherein the first DC output voltage turns on the fourth diode for maintaining the DC output voltage of the parallel power supply system at the predetermined value when the first DC output voltage is greater than the predetermined value, and the second DC output voltage turns on the third diode for maintaining the DC output voltage of the parallel power supply system at the predetermined value when the second DC output voltage is greater than the predetermined value.
Preferably, the first power supply further includes a low pass filter having one end electrically connected to the output terminal of the first power supply for filtering the first DC output voltage, and the other end electrically connected to ground.
Preferably, the first power supply further includes a first transformer which is a main power source of the first power supply.
Preferably, the first voltage feedback controller further includes a first isolated transformer having a primary side electrically connected to an output terminal of the first voltage feedback controller for providing an isolated protection.
Preferably, the first transformer further includes a switch electrically connected to a primary side of the first transformer for controlling the first DC output voltage by the first control signal.
Alternatively, the first power supply further includes a first buck converter which is a main power source of the first power supply.
Preferably, the first buck converter further includes a switch electrically connected to the first voltage feedback controller for controlling the first DC output voltage by the first control signal.
The present invention may best be understood through the following description with reference to the accompanying drawings, in which: